NYCPHP Meetup

[Joe Crawford]

wow too advanced in the math area for me lol

Joe Crawford Jr.

On Sun, 2004-07-18 at 20:31, Steve Manes wrote:
> Kshitij Bedi wrote:
> 
> > I have a database with zipcodes and corresponding latitudes and longitudes.
> > Can anyone suggest a mysql statement that can pull me all zipcodes within 20
> > or 50 or 100 miles of a given zipcode
> 
> You can do it as an imprecise rectangle, where latitude/longitude is 
> plus/minus a certain number of minutes.  Then you just do a SELECT for 
> all zipcodes where the longitude/latitude falls within that rectangle. 
> That's what a lot of job boards do and it usually works well enough for 
> estimation, especially insofar as the longitude/latitude in those 
> zipcode databases are only rough centers of mass.  Otherwise, if you 
> need more precision you'll need to use spherical geometry, which is very 
> costly.
> 
> Developers typically use either the ragged rectangle or precalculate 
> distances at fixed deltas, caching the results in a separate table.  You 
> get into some hairy calulus here because at higher latitudes the 
> distance between two longitudinal degrees decreases.  At the equator, 
> one degree of latitude or longitude is ~70 square miles, with 
> longitudinal distance decreasing to zero at the poles.
> 
> distance = 3959 * (
> 	sin(latitude1/57.3) * sin(latitude2/57.3) +
> 	cos(latitude1/57.3) * cos(latitude2/57.3) *
>          cos(longitude2/57.3 - longitude1/57.3))
> 
> Or something like that.
> 
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